1. Field of the Invention
The present invention relates to a thermal head and an electronic apparatus incorporating the thermal head, such as a facsimile machine, printer, plotter, word processor or the like.
2. Description of the Related Art
A thermal head is generally known which comprises a head or drive substrate, a plurality of heating elements disposed on the substrate in longitudinal and transverse lines, a drive element on the substrate for energizing the heating elements, a shift register on the substrate for receiving and storing data to be printed, and a plurality of integrated driving circuits (drive IC) on the substrate, these drive IC's including various circuits such as a latch circuit for holding the data to be printed stored in the shift register to provide them to the drive element. In the thermal head of such a type, the number of heating elements is very large (e.g. 2048). Thus, the heating elements are separately driven by using a plurality of strobe signals to actuate the drive element in a time shared manner for every block of strobe signals. Thus, the maximum current passing through the thermal head is equal to a current flowing through the total dots (heating elements) in one strobe which is divided by the strobe signal.
Electronic apparatus using the thermal head, such as facsimile machines, are desired to be reduced in size and cost as they are becoming more widespread. Therefore, the thermal heads are also required to be reduced in power and size.
As described, the maximum current passing through the prior art thermal head depends on the current flowing through the total number of dots in one strobe. Therefore, the time normally required to make the printing cannot be prolonged beyond a given length, resulting in the maximum current which cannot be reduced below a given level. On the other hand, if the printing rate is lower and the number of dots to be energized is smaller, the current decreases to provide a sufficient margin in power capacity. This provides a large difference in power between the higher and lower printing rates. In other words, the maximum current passing through the prior art thermal head depends on the total number of dots capable of being energized in one strobe. Thus, the prior art thermal head requires a power capacity meeting the maximum current. As a result, the size, weight and cost of power source could not be reduced below a certain level.